1. Field of the Invention
The present invention relates to a method of determining the lethality of defects in the circuit pattern inspection, a method of selecting defects to be treated as review objects, and the circuit pattern inspection system involved with these methods. Particularly, the invention relates to a method of efficiently determining, in a manufacturing process to form semiconductor devices on a semiconductor wafer, whether a defect detected by an appearance/particle inspection instrument is lethal in accordance with the characteristics of circuit patterns of the semiconductor devices, a method of efficiently selecting a defect that should be treated as a review object when defects are detected, in accordance with the characteristics of defects generated on each process, and the system involved with the above methods.
2. Description of the Related Art
In the semiconductor manufacturing process, it is essential for maintaining or enhancing the yield to detect the cause of a failure as quickly as possible and feedback the countermeasure to the process and/or the manufacturing facilities. In order to establish the countermeasure, it is important to detect a failure by an inspection instrument and analyze the inspection data.
As the conventional technique in this field, defects such as pattern shorts and a pattern missing which are generated on the wafer process, and particles are automatically inspected by, for example, the inspection instruments using an image processing and dark field irradiation by laser beams.
These inspection instruments output the coordinate data of defects and particles in the semiconductor wafer, and the sizes of the defects to an analysis system that stores these data. Next, the inspected wafer is moved onto a stage of an optical microscope or scanning electron microscope, the stage is moved to the position corresponding to the coordinate data of a detected defect, and the defect is classified by the magnified image thereof. This classification work is called the review.
This review has two objects.
One is to classify defects detected in accordance with the characteristics of the defects themselves, such as pattern missing, pattern shorts, film residue, particles, etc.
Another one is to determine whether a defect leads to a lethal defect for the function of the semiconductor device, and from the result to classify the defect into a lethal defect or non-lethal defect.
After completing the review, a review station outputs the classification identifiers predetermined in accordance with the classification and lethality/non-lethality of the defects themselves to the analysis system that analyzes the data.
The foregoing conventional technique has become an essential technique for enhancing the yield when forming circuit patterns on a semiconductor wafer through the micro fabrication.
On the process of manufacturing a semiconductor wafer, if a defect is detected, occasionally the defect cannot be any obstacle to the operation. If there are particles on the wafer, to regard all the semiconductor chips made therefrom as failure is to treat even the normally operating chips as failure. That is impractical.
Therefore, the determination as to whether the defect is lethal or not is specially important in the inspection process. However, the conventional technique involves the following problems in the determination of the defect being lethal or not.
In the conventional technique, the review and the determination of lethality are carried out by human hands and brains, and therefore, the work needs a considerable time, which will become a hindrance to enhancing the throughput of the total inspection process.
In regard to the determination of lethality, the inspector needs to have the knowledge of functions and structures of the circuit patterns of a defective area as well as the discrimination of the defects themselves, and the work is entrusted to specialists having those specific knowledge. Further, the determination criterion of lethality differs among these specialists, and the result of determination varies depending on the inspector, which is a problem.
If the determination of lethality by the review is not conducted at all on the pretext of the throughput, or the determination of only a part of defects is conducted, the following inconveniences will arise.
This problem will be described with reference to FIG. 19. FIG. 19 illustrates a graph in which a relation between the total number of defects and the yield is plotted, and a graph in which the total number of defects produced in time series on each of inspection wafers is plotted.
As shown in FIG. 19 (a), there is not a correlation between the total number of defects and the yield of the semiconductor chips, and thereby a significant control limit cannot be introduced. Here, the control limit signifies the number of defects that is provided for controlling the quality. The yield indicates the rate of non-defectives against all the chips on a wafer.
Accordingly, as shown in FIG. 19 (b), although the total defect number by each inspection wafer is plotted in time series to thereby predict the abnormality of the yield and to thereby take a countermeasure in an earlier stage, since the total defect number does not function as a monitor value, the setting of a control limit will not bring about a good detection of abnormality. In the example of this drawing, since the total defect number exceeds the control limit in every point, all the defects are to be determined as abnormal.
During the review, it is necessary to view an enlarged image by the optical microscope or scanning electron microscope, which accompanies the works of moving the stage, bringing the defect into the field of view, focusing and the like. Therefore, to carry out the reviews of all the defects detected by the inspection instrument will be a contradiction against the requirement for enhancing the throughput in the inspection process. Accordingly, it is necessary to reduce the number of the defects of the review object, however, this work to reduce the number is entrusted to the review operator; and the selection results of the review object will differ depending on the operators, which is a problem.
The present invention has been made to resolve the foregoing problems, and it is therefore an object of the invention to provide a method of determining the lethality of defects, which enhances the efficiency of inspection by automatically determining the lethality of defects without conducting the review when inspecting circuit patterns formed on a substrate of a semiconductor wafer or the like, and an inspection system to implement the same.
Another object of the invention is to provide a method of automatically selecting defects to be reviewed in order to efficiently perform the review in the inspection of the circuit patterns while maintaining the quality of the inspection itself, and an inspection system to implement the same.
In order to accomplish the foregoing objects, the invention sets forth a construction relating to a method of determining a lethality of defects in an inspection of circuit patterns formed on a substrate, as follows. At an inspection stage, inspection data of the defects produced on the circuit patterns are generated, the inspection data generated are inputted to be processed; and thereby, the lethality of the defects corresponding to the inspection data are determined.
In detail, the foregoing method of determining the lethality employs the coordinate data of the circuit patterns and the sizes of the defects as the inspection data.
Further in detail, the foregoing method of determining the lethality of defects segments each of the circuit patterns into several areas having different characteristics, and serves the data to determine the lethality of the defects as determination rules each provided for each of the areas of the circuit patterns.
To achieve the foregoing objects, the invention sets forth a further detailed construction relating to the method of determining a lethality of defects, as follows. When each of the circuit patterns is segmented into several areas having different characteristics, area coordinate data of the circuit patterns and data to determine the lethality of the defects produced in the areas on the circuit patterns are held, and the coordinate data of the defects detected and the sizes of the defects can be obtained at an inspection stage, the method of determining of a lethality of defects comprises the following steps.
(1) accepting the area coordinate data of the circuit patterns,
(2) accepting the data to determine the lethality of the defects produced in the areas on the circuit patterns,
(3) accepting the coordinate data of the defects detected on the circuit patterns and the sizes of the defects,
(4) identifying the areas to which the defects belong, from the coordinate data of the defects detected on the circuit patterns, and
(5) comparing the sizes of the defects detected with the data to determine the lethality of the defects produced in the areas on the circuit patterns where the defects belong to thereby determine the lethality of the defects. After the step (1) through the step (3), the step (4) is executed, and thereafter the step (5) is executed.
In detail, the foregoing method of determining a lethality employs length data, area data, and brightness data which are served as indexes when detecting the defects as the sizes of the defects.
Further in detail, the foregoing method of determining a lethality employs pattern widths or pattern spaces in the areas as the data to determine the lethality of the defects produced in the areas on the circuit patterns.
Further in detail, in the foregoing method of determining a lethality, when the area coordinate data of the circuit patterns and pixel coordinates for display are brought into correspondence and inherent class values according to the characteristics of the areas are individually assigned to each of the areas, the foregoing step (4) is comprised of the steps of:
(4a) writing in advance class values in an array to express pixel coordinates,
(4b) obtaining the pixel coordinates corresponding to the coordinate data of the defects detected, and
(4c) determining the areas where the defects belong from the pixel coordinates.
To achieve the foregoing objects, the invention sets forth a construction relating to a method of selecting a review object of defects detected in an inspection of circuit patterns formed on a substrate, as follows. At an inspection stage, inspection data of the defects produced on the circuit patterns are generated, the inspection data generated are inputted to be processed; and thereby, the data to determine the lethality of the defects corresponding to the inspection data are generated, and the data to determine the lethality of the defects and the inspection data are compared, and thereby, the review object is selected among the defects produced.
In detail, the foregoing method of selecting a review object employs the coordinate data of the circuit patterns and the sizes of the defects as the inspection data.
Further in detail, the foregoing method of selecting a review object segments each of the circuit patterns into several areas having different characteristics, and serves the data to determine the lethality of the defects as determination rules each provided for each of the areas of the circuit patterns.
To achieve the foregoing objects, the invention sets forth a further detailed construction relating to the method of selecting a review object, as follows. When each of the circuit patterns is segmented into several areas having different characteristics, area coordinate data of the circuit patterns and data to determine the lethality of the defects produced in the areas on the circuit patterns are held, and coordinate data of the defects detected and sizes of the defects can be obtained at an inspection stage, the method of selecting a review object comprises the following steps.
(11) accepting the area coordinate data of the circuit patterns,
(12) accepting the data to determine the lethality of the defects produced in the areas on the circuit patterns,
(13) accepting the coordinate data of the defects detected on the circuit patterns and the sizes of the defects,
(14) identifying the areas to which the defects belong, from the coordinate data of the defects detected on the circuit patterns, and
(15) calculating ratios of the sizes of the defects detected against the data to determine the lethality of the defects produced in the areas on the circuit patterns where the defects belong. After the step (11) through the step (13), the step (14) is executed, thereafter the step (15) is executed, and the review object is selected, while the ratios are served as the indexes to indicate severity of the defects.
In detail, in the foregoing method of selecting a review object, the defects selected as the review object are confined to the defects corresponding to a specific number of the ratios obtained at the step (15), sorted in the descending order.
Further in detail, in the foregoing method of selecting a review object, the defects selected as the review object are the defects corresponding to the ratios which are obtained at the step (15) and have respectively a specific value or more.
Further in detail, the foregoing method of selecting a review object employs length data, area data, and brightness data which are served as indexes when detecting the defects as the sizes of the defects.
Further in detail, the foregoing method of selecting a review object employs pattern widths or pattern spaces in the areas as the data to determine the lethality of the defects produced in the areas on the circuit patterns.
Further in detail, in the foregoing method of selecting a review object, when the area coordinate data of the circuit patterns and pixel coordinates for display are brought into correspondence and inherent class values according to the characteristics of the areas are individually assigned to each of the areas, the foregoing step (14) is comprised of the steps of:
(14a) writing in advance class values in an array to express pixel coordinates,
(14b) obtaining the pixel coordinates corresponding to the coordinate data of the defects detected, and
(14c) determining the areas where the defects belong from the pixel coordinates.
Further in detail, the foregoing method of selecting a review object, in selecting the defects treated as the review object for each process, further comprises a step that compares coordinate data of the defects having been detected as the defects in a previous process to a process where the review is being executed at present with coordinate data of the defects having been detected as the defects in the concerned process where the review is being executed at present, and selects only the defects having non-coincident coordinate data in the result of the comparison as candidate defects of the review object in the concerned process where the review is being executed.
Further in detail, the foregoing method of selecting a review object further comprises a step that classifies the defects produced on the circuit patterns into cluster defects having a clustered mode and random defects produced at random from the mode in which the defects are produced, and selects the review object with different treatments for the cluster defects and the random defects.
Further in detail, the foregoing method of selecting a review object selects several defects of the cluster defects as the review object, and assumes the review result of the several defects as the review result of all the defects belonging to the cluster to thereby simplify the review for the cluster defects.
Further in detail, the foregoing method of selecting a review object, in selecting the defects treated as the review object for each process, when the cluster defects detected in the previous process and the cluster defects detected in the subsequent process have an overlapping part, treats both of the cluster defects as the cluster defects detected in the previous process.
In order to accomplish the foregoing objects, the invention sets forth a system of determining a lethality of defects in an inspection of circuit patterns formed on a substrate, which comprises: means to input inspection data of the defects produced on the circuit patterns, which are detected at an inspection stage; means to process the inspection data inputted; and means to determine the lethality of the defects corresponding to the inspection data.
In detail, the foregoing system of determining a lethality employs the coordinate data of the circuit patterns and the sizes of the defects as the inspection data.
Further in detail, the foregoing system of determining the lethality segments each of the circuit patterns into several areas having different characteristics, and serves the data to determine the lethality of the defects as determination rules each provided for each of the areas on the circuit patterns.
To achieve the foregoing objects, the invention sets forth a further detailed construction relating to the method of determining a lethality of defects, as follows. When each of the circuit patterns is segmented into several areas having different characteristics, the system comprises: an inspection instrument that obtains coordinate data of the defects detected and sizes of the defects, and an analysis system that analyzes the data to determine the lethality. The analysis system here includes a control unit, a memory to temporarily hold the data, a storage unit to permanently store the data, an operation unit, and an input/output interface. The analysis system further comprises: means to store the area coordinate data of the circuit patterns; means to store the data to determine the lethality of the defects produced in the areas on the circuit patterns; means to store the coordinate data of the defects detected on the circuit patterns and the sizes of the defects; means to identify the areas to which the defects belong, from the coordinate data of the defects detected on the circuit patterns; and means to compare the sizes of the defects detected with the data to determine the lethality of the defects produced in the areas on the circuit patterns where the defects belong to thereby determine the lethality of the defects.
In detail, the foregoing system of determining a lethality employs length data, area data, and brightness data which are served as indexes when detecting the defects as the sizes of the defects.
Further in detail, the foregoing system of determining a lethality employs pattern widths or pattern spaces in the areas as the data to determine the lethality of the defects produced in the areas on the circuit patterns.
Further in detail, in the foregoing system of determining a lethality, the inspection instrument and the analysis system are connected by a network, so that the data and commands can be exchanged.
Further in detail, in the foregoing system of determining a lethality, when the area coordinate data of the circuit patterns and pixel coordinates for display are brought into correspondence and inherent class values according to the characteristics of the areas are individually assigned to each of the areas, the analysis system, further containing a pixel coordinate storage unit, comprises means to write class values in an array to express the pixel coordinates, means to obtain the pixel coordinates corresponding to the coordinate data of the defects detected, and means to determine the areas where the defects belong from the pixel coordinates.
In order to accomplish the foregoing objects, the invention sets forth a system of selecting a review object of defects detected in an inspection of circuit patterns formed on a substrate, which comprises: means to input inspection data of the defects produced on the circuit patterns, which are detected at an inspection stage; means to process the inspection data inputted; means that generate the data to determine the lethality of the defects corresponding to the inspection data; and means that compare the data to determine the lethality of the defects with the inspection data. The system selects the review object among the defects produced, by using the means that compare the data to determine the lethality of the defects with the inspection data.
In detail, the foregoing system of selecting a review object employs the coordinate data of the circuit patterns and the sizes of the defects as the inspection data.
Further in detail, the foregoing system of selecting a review object segments each of the circuit patterns into several areas having different characteristics, and serves the data to determine the lethality of the defects as determination rules each provided for each of the areas of the circuit patterns.
In order to accomplish the foregoing objects, the invention sets forth a further detailed system of selecting a review object, which comprises: an inspection instrument that obtains coordinate data of the defects detected and sizes of the defects; and an analysis system that analyzes the data to select the review object. The analysis system includes a control unit, a memory to temporarily hold the data, a storage unit to permanently store the data, an operation unit, and an input/output interface, which further comprises: means to store the area coordinate data of the circuit patterns; means to store the data to determine the lethality of the defects produced in the areas on the circuit patterns; means to store the coordinate data of the defects detected on the circuit patterns and the sizes of the defects; means to identify the areas to which the defects belong, from the coordinate data of the defects detected on the circuit patterns; and means to calculate the ratios of the sizes of the defects detected against the data to determine the lethality of the defects produced in the areas on the circuit patterns where the defects belong. With this construction, the system of selecting a review object of the invention selects the review object, using the ratios as the indexes to indicate severity of the defects.
In detail, in the foregoing system of selecting a review object, the defects selected as the review object are confined to the defects corresponding to a specific number of the ratios obtained by the means to calculate the ratios, sorted in the descending order.
Further in detail, in the foregoing system of selecting a review object, the defects selected as the review object are the defects corresponding to the ratios obtained by the means to calculate the ratios and have respectively a specific value or more.
Further in detail, the foregoing system of selecting a review object employs length data, area data, and brightness data which are served as indexes when detecting the defects as the sizes of the defects.
Further in detail, the foregoing system of selecting a review object employs pattern widths or pattern spaces in the areas as the data to determine the lethality of the defects produced in the areas on the circuit patterns.
Further in detail, the foregoing system of selecting a review object further comprises a review station to perform the review; and the review station, the inspection instrument, and the analysis system are connected by a network, so that the data and commands can mutually be exchanged.
Further in detail, in the foregoing system of selecting a review object, the analysis system, further containing a pixel coordinate storage unit, comprises means to write class values in an array to express the pixel coordinates, means to obtain the pixel coordinates corresponding to the coordinate data of the defects detected, and means to determine the areas where the defects belong from the pixel coordinates.
Further in detail, the foregoing system of selecting a review object, in selecting the defects treated as the review object for each process, further comprises means that compare coordinate data of the defects having been detected as the defects in a previous process to a process where the review is being executed at present with coordinate data of the defects having been detected as the defects in the concerned process where the review is being executed at present, and selects only the defects having non-coincident coordinate data in the result of the comparison as candidate defects of the review object in the concerned process where the review is being executed.
Further in detail, the foregoing system of selecting a review object further comprises means that classify the defects produced on the circuit patterns into cluster defects having a clustered mode and random defects produced at random from the mode in which the defects are produced, and selects the review object with different treatments for the cluster defects and the random defects.
Further in detail, the foregoing system of selecting a review object selects several defects of the cluster defects as the review object, and assumes the review result of the several defects as the review result of all the defects belonging to the cluster to thereby simplify the review for the cluster defects.
Further in detail, the foregoing system of selecting a review object, in selecting the defects treated as the review object for each process, when the cluster defects detected in the previous process and the cluster defects detected in the subsequent process have an overlapping part, treats both of the cluster defects as the cluster defects detected in the previous process.
Based on the foregoing construction of the invention, the following effects will be achieved.
The foregoing method of determining a lethality makes it possible to automatically determine the lethality of the defects detected by the inspection instrument, without making a review of an enlarged image by using an optical microscope or scanning electron microscope. Accordingly, the determination of the lethality of the defects can be carried out at a high speed, and the lethality of all the defects detected can be determined.
Here, the advantage to determine the lethality of defects will be explained with reference to FIG. 20.
FIG. 20 illustrates a graph in which the relation between the number of defects determined as lethal and the yield is plotted, and a graph in which the number of defects determined as lethal that are produced in time series for each inspection wafer is plotted.
To determine the lethality of defects is to weight with a filter the defects determined as lethal from all the defects detected. If the lethality of the defects is determined and the number of the defects determined as lethal is obtained, as shown in FIG. 20 (a), the number of the defects determined as lethal is found to possess a correlation with the yield of the chips. Therefore, a control limit can be introduced from the value of the yield, which is different from the case with the total defect number as shown in FIG. 19.
Accordingly, to control the abnormality of each inspection wafer with the number of the defects determined as lethal will detect abnormalities with a high accuracy. As shown in FIG. 20 (b), when the number of lethal defects exceeds the control limit, the inspection wafer can be determined as abnormal. Thus, based on the control by the number of lethal defects, it becomes possible to detect abnormalities having correlation with the yield with a high accuracy, and thereby a countermeasure to raise the yield can be taken in an earlier stage.
In the foregoing description, the number of lethal defects is employed to control abnormalities, however, the rate of lethal defects may be employed. Here, the rate of lethal defects is the ratio of the number of the chips having lethal defects against the number of all the chips formed on the wafer.
Further, to correlate the area coordinates with the pixel coordinates, and assign in advance the class values to the pixel coordinate data makes it possible to swiftly determine the areas where the defects produced belong.
Next, according to the method of selecting a review object of defects detected in an inspection of circuit patterns of the invention, it becomes possible to automatically select a review object in the order of the importance of the review. Accordingly, the review can be performed with a high efficiency, while maintaining the quality of the review.
Further, the method of selecting a review object of the invention has a step that stores the coordinate data of the defects detected and the size data thereof, and thereafter, compares the coordinate data of the defects detected in the previous process with the coordinate data of the defects detected in the concerned process, and selects only the defects having non-coincident data as the defects produced in the concerned process.
Thereby, the defects already reviewed in the previous process cannot be selected again, thus avoiding a useless work.
Further, the method of selecting a review object of the invention has a step that classifies the defects having non-coincident coordinate data of the defects detected in the previous process and the defects detected in the concerned process into cluster defects and random defects from the coordinate data of the defects detected, and selects the defects to be reviewed from the defects thus classified.
Accordingly, the defects belonging to the same cluster that should be treated as the same classification cannot be selected repeatedly as the review object, thus eliminating a useless work.
Furthermore, the method of selecting a review object of the invention has a step that, after the classification of the cluster defects and random defects in the concerned process, compares the coordinate data of the cluster defects detected in the previous process with those of the cluster defects detected in the concerned process, and when the coordinate data of the cluster defects detected are coincident in more than one, puts all the defects contained in the clusters of the cluster defects in the previous process and the cluster defects in the concerned process into the same classification.
Thereby, the defects produced in the concerned process that result from the cluster defects produced in the previous process can be excluded from the review object, and a review result can be obtained with efficiency.